/**
 * LCR 173. 点名
 * https://leetcode.cn/problems/que-shi-de-shu-zi-lcof/description/
 */
class Solution3 {
    public int takeAttendance(int[] records) {
        int n = records.length;
        int left = 0, right = n - 1;
        
        while(left < right) {
            int mid = left + (right - left) / 2;
            if(records[mid] == mid) left = mid + 1;
            else right = mid;
        }

        return left == records[left] ? left + 1 : left;
    }
}